Two-phase process for preparing poly(vinyl alcohol)-co-poly(vinylamine)

ABSTRACT

Vinyl acetate and an N-vinyl formamide are copolymerized to yield poly(vinyl acetate)-co-poly(N-vinyl formamide) which is base hydrolyzed to poly(vinyl alcohol)-co-poly(N-vinyl formamide). Two phase hydrolysis of particles of poly(vinyl alcohol)-co-poly(N-vinyl formamide) as a slurry in methanol yields particles of poly(vinyl alcohol)-co-poly(vinylamine). 
     Provided is a copolymer of the following general formula ##STR1## where m is 0 to 15 mole %, 
     n is 50 to 99 mole %, x is 0 to 30 mole %, and y is 1 to 50 mole %.

This is a division of application Ser. No. 07/181,887 filed Apr. 15,1988.

TECHNICAL FIELD

The invention relates to amine functional polymers and, moreparticularly, the invention relates to copolymers containing vinylalcohol and vinylamine units.

BACKGROUND OF THE INVENTION

Synthesis of amine functional addition polymers in general is difficultfor two reasons. The simplest amine functional monomer, vinylamine, isthermodynamically and kinetically unstable relative to the isomericSchiff base and condensation products of the base, ethylidene imine.Also, more complex molecules containing free radically polymerizablefunctionality, e.g., olefinic groups, and primary amine functionalityare more expensive and typically show severe chain transfer duringradical polymerization, especially involving protons on carbon atomsalpha to the nitrogen. The allylamines are particularly good examples ofthis difficulty and are known to produce mainly low molecular weightpolymers and copolymers, even using large amounts of free radicalinitiators.

Despite these problems, amine containing polymers are highly valued in anumber of areas. They represent virtually the only cost effective way ofincorporating cationic charge into polymers for, e.g., cationicelectrocoating, water treatment and enhanced oil recovery, primary and,to a lesser extent, secondary amines offer the highest generalreactivity spectrum of any group compatible with water. They will reactwith anhydrides, epoxides, isocyanates, esters, aziridines, aldehydes,ketones, Michael acceptors, aminoplasts and other alkylating agents toform covalent linkages. They react with acids and metal ions to formionic linkages. Simple derivatives, e.g., Schiff bases, strongly andselectively complex many metal ions. This high reactivity produces amyriad of current and potential uses in such areas as coatings,adhesives, binders, structural polymers, viscosity control agents, ionexchange resins, and polymer boundary agents for bio/medicalapplications.

Because of their high electron donating ability when unprotonated andcationic charge when protonated, they offer superior adhesion to manytypes of substrates compared to other polymers which are typicallyneutral or anionic. The ability to change the reactivity and propertiesof primary or secondary amines by a simple pH change (addition of acidor base) offers numerous valuable options for viscosity control,emulsion stability control, polymer solubility modification (especiallyin water), or for formulating shelf-stable but reactive crosslinking orsubstrate reactive systems.

For many purposes it is desirable to prepare water soluble polymerswhich contain relatively low levels of amine functionality, either toreduce costs by diluting the expensive amine component or forapplications in which a lower level of cationic or reactive amine givessuperior performance. A particularly attractive polymer for certainapplications would be a vinyl alcohol copolymer with a low butcontrollable level of amine functionality.

Preparation of amine functional polyvinyl alcohol (PVOH) has beenpreviously attempted by hydrolyzing copolymers of vinyl acetate andeither N-vinyl-O-t-butyl carbamate or N-vinylacetamide. The carbamatemonomer is prepared by a long and costly synthesis and is reported tohydrolyze to a highly toxic aziridine in the presence of water. In bothcases the poly(vinyl acetate) component was hydrolyzed with methanolicor aqueous base. In the carbamate case, treatment of an aqueous solutionof the poly(vinyl alcohol)-co-poly(N-vinyl-O-t-butyl carbamate) withacid gave the poly(vinyl alcohol)-co-poly(vinylamine) acid salt.Hydrolysis of the poly(N-vinylacetamide) is known to require strong acidat high temperatures. Both approaches produce a relatively diluteaqueous solution of the polymer which is expensive to store or ship orrequires expensive additional steps to isolate the polymer from thesolution. The aqueous solution also contains substantial amounts offrequently undesirable salts or acid.

R. W. Stackman. et. al., Ind. Eng. Chem. Prod. Res. Dev., 1985, 24, 242discloses copolymerization of vinyl acetate with N-vinylacetamide andcopolymer hydrolysis, probably to the poly(vinylalcohol)-co-poly(N-vinylacetamide). See R. H. Summerville, et al.,polymer Reprints, 24, 12 (1983).

W. M. Brouwer, et al.; J. Polym. Sci. Polym. Chem. Ed., 1984, 22, 353discloses copolymerization of vinyl acetate with N-vinyl-O-t-butylcarbamate and copolymer hydrolysis.

SUMMARY OF THE INVENTION

The present invention provides, for the first time, an industriallyattractive process for synthesizing poly(vinylalcohol)-co-poly(vinylamine) [PVOH/PVAm] by the unexpected two phasehydrolysis of solvent swollen particles of poly(vinylalcohol)-co-poly(N-vinyl formamide) [PVOH/PNVF] in methanol. Acidhydrolysis provides a cationic product while previously unknown basehydrolysis yields a salt free amine functional vinyl alcohol copolymer.

Although hydrolysis of amides is difficult and reactions in two-phasepolymer/liquid systems with poor accessibility of polymer sites isnotoriously difficult, surprisingly, the present process provides forthe efficient hydrolysis of vinyl alcohol/N-vinyl formamide copolymerparticles in a two phase system yielding PVOH/PVAm particles which canbe readily isolated by filtration. Since it is not necessary to dissolvethe PVOH/PNVF in order to perform the hydrolysis of the amidefunctionality of the copolymer, it is not necessary to precipitate thehydrolyzed product again.

As a preferred embodiment the overall process for preparing thePVOH/PVAm would comprise the following steps:

(a) continuously feeding vinyl acetate monomer and N-vinyl formamidemonomer into a reaction mixture in a reaction vessel,

(b) copolymerizing the vinyl acetate and N-vinyl formamide to yieldpoly(vinyl acetate)-co-poly(N-vinyl formamide) [PVAc/PNVF] in thereaction mixture,

(c) continuously withdrawing from the reaction vessel reaction mixturecontaining the PVAc/PNVF,

(d) hydrolyzing the acetate functionality of the PVAc/PNVF in amethanolic medium to yield a vinyl alcohol copolymer as a gel swollenwith methanol and methyl acetate,

(e) comminuting the gel to give a particulate copolymer product andoptionally rinsing with methanol,

(f) hydrolyzing the copolymer particles as a slurry in methanol withacid or base to give PVOH/PVAm particles, and optionally but preferably,

(g) washing the particulate PVOH/PVAm with methanol to remove solublesalts and by-products and removing the solvent from the copolymerproduct, especially by vacuum or thermal stripping.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a modified polyvinyl alcohol compositioncomprising a copolymer of vinyl alcohol, optionally vinyl acetate and/orvinyl formamide, and vinylamine of the following general formula I.##STR2## wherein m=0-15 mole %,

n=50-99 mole %,

x=0-30 mole %, preferably 0.5-10 mole % and

y=1-50 mole %, preferably 1-25 mole %;

preferably

m=0-2 mole %,

n=70-95 mole %.

x=0.5-10 mole %, and

y=1-25 mole %.

most preferably

m=0-2 mole %

n=85-95 mole %

x=0.5-4 mole %; and

y=5-12 mole %

For purposes of describing the invention, the copolymer of formula 1will be considered poly(vinyl alcohol)-co-poly(vinylamine) and referredto as PVOH/PVAm. Nevertheless, it is to be understood that PVOH/PVAm maycontain some vinyl alcohol units as the acetate ester; i.e. vinylacetate units. Contemplated as the functional equivalent of vinylacetate for the purposes of this invention are vinyl esters of formicacid and C₃ -C₁₂ alkanoic acids, benzoic acid and trifluoroacetic acid.In addition, PVOH/PVAm may also contain some vinylamine units as theunhydrolyzed formamide, i.e N-vinyl formamide units. Contemplated as thefunctional equivalent of N-vinyl formamide for purposes of thisinvention are vinylamides such as N-vinyl trifluoroacetamide and thosein which the nitrogen is substituted with a C₁ -C₄ alkyl or2-hydroxyalkyl group.

The PVOH/PVAm polymers of the invention have an average molecular weight(Mw) ranging from about 10,000 to 200,000, preferably 15,000 to 130,000.

The copolymers of the invention are prepared by a free radicalcontinuous or batch polymerization process. The continuous process givesmore uniform molecular weight distribution and uniformity of comonomerincorporation (i.e. a substantially random homogeneous copolymer),improves the lot-to-lot uniformity and offers the commercialattractiveness of continuous operation. The batch process allowsproduction in simple batch equipment and may be carried to highconversion to avoid monomer stripping.

Suitable free radical initiators for the polymerization reaction wouldinclude organic peroxides such as t-butyl peroxypivalate,di(2-ethylhexyl)peroxydicarbonate, t-butyl peroxyneodecanoate and2,2'-azobisisohexyl)peroxydicarbonate, butyronitrile. The concentrationof the initiator in the polymerization reaction mixture will normallyrange from 0.0001-2 wt %, the preferred concentration being 0.001-0.5 wt%.

Preferably the polymers are prepared using a train of continuous stirredtank reactors followed by a hydrolysis, or alcoholysis, reaction. Vinylacetate, N-vinyl formamide, free radical initiator and methanol areadded continuously to the first reactor. The N-vinyl formamide comonomercan be added to subsequent reactors in order to maintain a homogeneouscopolymer.

Unreacted vinyl acetate is removed from the exit stream by contacting itwith methanol vapors in a stripping column yielding an intermediatevinyl acetate random copolymer [PVAc/PNVF] having the general formulaII. ##STR3## wherein m=50-99 mole % and

x=1-50 mole %.

The alcoholysis of the intermediate PVAc/PNVF copolymer is effected bythe addition of a base catalyst. The resulting solid PVOH/PNVF gelswollen by methanol and methyl acetate is ground to give a granularproduct and rinsed with fresh methanol to remove methyl acetate. ThePVOH/PNVF has the following general formula III ##STR4## wherein m is0-15 mole %, preferably 0-2 mole % for subsequent base hydrolysis to thevinylamine copolymer.

n is 50-99 mole %, and

x is 1 to 50 mole %.

A suitable process for preparing the PVAc/PNVF and subsequent hydrolysisto PVOH/PNVF is essentially like the process described in U.S. Pat. No.4,675,360 directed to vinyl alcohol/poly(alkyleneoxy) acrylatecopolymers, the disclosure which is hereby incorporated by reference.

Stripping of unreacted vinyl acetate is most conveniently done forcontinuous processes by countercurrent contacting of the polymer pastesolution with hot solvent. Stripping may be avoided by fully convertingthe monomers as in many batch processes. Hydrolysis without priorremoval or reduction of vinyl monomer by polymerization or otherchemical reaction tends to produce unacceptable levels of acetaldehydeand its condensation products. These in turn produce color and maycrosslink PVOH or PVAm groups, reducing polymer solubility. N-vinylformamide or other vinyl amides are more difficult to remove from thesolution polymer, but their higher reactivity than vinyl acetate in thepolymerization and frequently lower levels of incorporation minimize theamounts of these monomers present in the final product.

The copolymers of the invention may also contain other comonomers, suchas for example, (meth)acrylate, crotonate, fumarate or maleate esters,vinyl chloride, ethylene, N-vinyl pyrrolidone, and styrene in amountsranging from about 2 to 20 mole %.

The hydrolysis of the PVAc/PNVF may be conducted batch or continuouslywith acid or base catalysis in various solvents. However it is mostconveniently done in methanol, optionally with various levels of water,via base catalyzed transesterification. The reaction gives methylacetate as a volatile coproduct and PVOH copolymer as a solvent swollenbut insoluble separate phase. The level of PVAc hydrolysis is adjustedby varying the base addition level and reaction time, but becomesessentially complete during base initiated PNVF hydrolysis in thesubsequent step. Higher levels of base catalyst (e.g., 1 to 3 mole % onPVAc groups in the copolymers with 6 to 12% PNVF) are required for thetransesterification reaction than are needed for PVAc homopolymers.

The transesterification solvent (for example methanol) level may bevaried over wide ranges which should exceed the amount required byreaction stoichiometry and preferably provide sufficiently low viscosityfor efficient mixing of added catalyst and for heat removal. Desirably,a powdery product may be obtained directly in a batch hydrolysis using avessel with efficient stirring by adding large amounts of methanol, forexample a 10-fold excess over PVAc copolymer, but high levels ofmethanol give lower polymer throughput or require larger equipment.Continuous hydrolysis of copolymer with base can be convenientlypracticed at 20-60% polymer solids by mixing the base catalyst with thealcohol solution of the copolymer and extruding the mixture onto amoving belt, much as is done commercially for the preparation of PVOHhomopolymer. The hydrolyzed polymer in the form of a methanol/methylacetate swollen gel is then ground and may be rinsed with fresh methanolto remove catalyst residues and methyl acetate. The resulting methanolswollen polymer can then be dried or, preferably, used as is in thesubsequent PNVF hydrolysis step.

The hydrolysis of PVOH/PNVF to PVOH/PVAm can be accomplished by base oracid hydrolysis. Base hydrolysis, preferably with alkali hydroxide (NaOHor KOH) or alkaline earth hydroxide, requires 0.7 to 3 times, preferably1 to 1.5 times, stoichiometric quantities based on PNVF, and is bestconducted at elevated temperatures (50°-80° C.). Although the base oracid hydrolysis reaction can be accomplished in aqueous solution, theproduct must then be recovered by precipitation or solvent evaporation.As a slurry of methanol swollen PVOH/PNVF particles in methanol, the twophase reaction is initially fast, but slows down after partialconversion, probably reflecting slow reaction with less accessibleformamide groups. Conversion after 24 hours is about 85% but can beraised to 93% by adding small amounts of water in amounts of 1 to 20 wt%, based on methanol. The slurry may comprise 10 to 65 wt %, preferably20 to 50 wt %, copolymer particles in methanol. Contemplated as thefunctional equivalent of methanol as the liquid medium of the slurry areC₂ -C₆ alkyl alcohols and diols and C₄ -C₈ alkyl ethers. The methanolmay also contain methyl acetate from the hydrolysis of the PVAccomponent. The two phase hydrolysis has the advantage that the productscan be separated from the liquid phase, rinsed, and dried to produce asalt-free primary amine functional PVOH in a commercially practicalprocess. The base hydrolysis reaction is best run on substantially fullyhydrolyzed [>98 mole %] PVOH copolymer. In the following Examples, Runs5A and B show that attempted hydrolysis of PVAc/PNVF with sufficientbase to also hydrolyze the formamide in a single step gave completeacetate transesterification, but no formamide hydrolysis, even when rununder pressure at elevated temperatures. This may reflect the reactionof the strong hydroxide or alkoxide base with PVAc to give a weaklynucleophilic acetate salt and water. The latter will transesterify PVAcbut not hydrolyze PNVF. Example VI, however, shows that, surprisingly,additional NaOH will successfully hydrolyze PVOH/PNVF powder product asa slurry in methanol containing methyl acetate from the first stagehydrolysis. Use of solvent swollen polymer particles from the prior PVAchydrolysis is believed to be beneficial in optimizing formamideaccessibility to base attack. The addition of water to the hydrolysismixture is believed to swell the polyvinyl alcohol, which improves thehydrolysis.

Obviously, shorter reaction times or substoichiometric quantities ofbase can be used to achieve lower levels of formamide hydrolysis asdesired.

Acid hydrolysis appears to give rapid and complete PNVF hydrolysis inthe copolymer when conducted at temperatures ranging from 15° to 80° C.Suitable strong acids would include the halogen acids, nitric acid,trifluoroacetic acid and methanesulfonic acid, with hydrochloric acidbeing preferred. Di- and higher valent acids such as sulfuric acid orphosphoric acid may also be suitable. Acid in 0.7 to 3 times, preferably1 to 1.5 times stoichiometry based on PNVF is required for thishydrolysis reaction with levels near stoichiometric preferred foravoiding post-neutralization of the excess acid. Again, although acidhydrolysis in aqueous solution is feasible, the reaction is preferablyperformed as a methanol suspension of PVOH/PNVF particles. However, fullhydrolysis of the acetate linkages and prior removal of methyl acetateare not required with the two phase acid hydrolysis.

Acid hydrolysis appears to be the preferred route to PVOH/PVAm.HX, i.e.where the charged ammonium salt product is acceptable or preferred.

Thus, N-vinyl formamide is used as an amine precursor whichcopolymerizes efficiently with structurally similar vinyl acetate underessentially industry-standard conditions and hydrolyzes efficientlyunder acid or base treatment in a methanol slurry to generate thermallystable reactive primary amines or ammonium salt groups along the polymerchain. Protection of the amine as the readily hydrolyzed formylderivative in particular allows surprisingly mild conditions in thefinal step.

The base hydrolysis step proceeds via essentially full hydrolysis of thePVAc component of the copolymer. The coproduced methyl acetate isoptionally removed by rinsing the ground, solvent swollen polymer withfresh solvent, and then hydrolysis of the still solvent swollenPVOH/PNVF particles is rapidly effected by alcohol soluble base. The useof a two phase system, i.e. use of a solvent in which the PVOH/PNVF andPVOH/PVAm are no longer soluble, allows the unreacted base and saltproducts to be removed by decantation and washing, with the copolymerreadily recovered in a granular solid form.

Alternatively, acid catalyzed hydrolysis of the ground, solvent swollenpolymer depends on protonation of the relatively basic formamidenitrogen to give a good leaving group which can be readily displaced bywater or alcohol to give a formate ester or formic acid as products.Unreacted excess acid, salts and by-product formic acid can be removedby decantation or filtration and washing to give a granular solidproduct.

EXAMPLE 1

The following continuous polymer paste process for making PVAc/PNVF usedtwo 2,000 ml jacketed reaction vessels and a surge vessel with bottomoutlets and a methanol stripper column. Each reaction vessel wasequipped with a stirrer, feed lines, thermocouple, nitrogen sparge lineand reflux condenser. The reaction vessels were connected in series by agear pump with variable speed motor. The methanol stripper was a 70cm×75 mm column, containing 8×8 mm Raschig rings in the top two thirdsand 6×6 mm Raschig rings in the bottom third. At the top of the columnwas a take-off condenser and a methanol boiler was connected to thebottom of the column.

Table 1 shows the initial charges that were added to reactors I and II.Continuous feeds 1, 2 and 3 were added to reactor I and feed 4 toreactor II. When the reactor temperatures approached 60° C. the feedswere begun. The flow rates from reactor I to reactor II and from reactorII to the paste collecting port were adjusted to maintain reactor I andreactor II levels. Free monomer (vinyl acetate and N-vinyl formamide) inreactors I and II was monitored periodically by a titration method,percent unreacted N-vinyl formamide was determined by gaschromatography. The amount of catalyst added into reactor I was variedto adjust percent vinyl acetate at steady state.

Once initial equilibrium was achieved, polymer paste was collected. Tomaximize paste yield at the end of a sequence, reactor I was cooled toambient and its feeds were discontinued but the feeds (including fromreactor I) to reactor II were maintained. When reactor I was empty, thefeed to reactor II was discontinued and the contents of reactor II werecooled and commingled with prima material.

Paste was poured or pumped continuously into the surge vessel and pumpedto the top of the heated methanol stripper for removal of vinyl acetate.The paste was restripped if necessary to achieve a vinyl acetate levelbelow 0.1%.

Run 1. Synthesis of PVAc/6% PNVF

    ______________________________________                                        Initial Charges (g) Reactor I                                                                              Reactor II                                       ______________________________________                                        N-vinylformamide (75% Basis)                                                                      21.3     7                                                Vinyl acetate (distilled)                                                                         460      248                                              Methanol            1,001    1,048                                            Lupersol 10         0.12     0.12                                             Tartaric Acid       0.02     0.02                                             ______________________________________                                        Feeds              g/h     mL/h                                               ______________________________________                                        1.     Vinyl acetate (dist)                                                                          370                                                                                   440                                                   N-Vinylformamide                                                                              21.3                                                          (Dist., 75%)                                                           2.     Methanol        150                                                                                   190                                                   Lupersol 10     0.43                                                   3.     Methanol        107                                                                                   135.5                                                 Tartaric acid   0.012                                                  4.     Vinyl acetate   12      12.35                                                 (Dist.)                                                                ______________________________________                                    

Reactor temperatures were 60°-63° C. throughout the polymerization. Ahigher molecular weight PVAc/6% PNVF paste was collected after initialequilibration when the concentration of vinyl acetate was 30-43% inreactor I and 22-35% in reactor II by titration.

"Prime" PVAc/6% PNVF paste was collected as the free monomerconcentration approached 20% in reactor II. Using a catalystconcentration of 0.67% in Feed 2, free monomer was 28 to 30% in reactorI and 16 to 19% in reactor II. Percent unreacted NVF was about 0.76% inreactor I and 0.22% in reactor II. Analysis of the polymer by nmr showeda PNVF:PVAc ratio of 1/16.1, i.e. 6.2% NVF.

Run 2. Synthesis of PVAc/12% PNVF

This run was identical to the previous one except for higher NVF andcatalyst ratios:

    ______________________________________                                        Initial Charges (g):                                                                          Reactor I   Reactor II                                        ______________________________________                                                      Paste from 6%                                                                           500 mL                                                              NVF reaction                                                                            methanol                                              ______________________________________                                        Feeds              g/h     mL/h                                               ______________________________________                                        1.     Vinyl acetate (dist)                                                                          369                                                                                   440                                                   N-Vinylformamide                                                                              42.6                                                          (Dist., 75%)                                                           2.     Methanol        150                                                                                   190                                                   Lupersol 10     1.0                                                    3.     Methanol        107                                                                                   135.5                                                 Tartaric acid   0.012                                                  4.     Vinyl acetate   12      13.8                                                  (Dist.)                                                                ______________________________________                                    

Reactor temperatures were 60°-63° C. throughout the polymerization.Higher molecular weight PVAc/12% PNVF paste was collected whenequilibrium was established and at a catalyst concentration of 1.3% inFeed 2. Free monomer concentration in reactor I was about 33 to 37% and23 to 29% in reactor II by titration. Percent unreacted NVF was about2.7% in reactor I and in reactor II.

Prime PVAc/12% PNVF paste was collected as the free monomerconcentration approached 22% in reactor II. (Catalyst in Feed 2 at1.3%). Free monomer was about 29 to 31% in reactor I and 15-22% inreactor II by titration. Unreacted NVF was about 1.45% in reactor I and0.4% in reactor II. NMR analysis of the polymer product indicatedPNVF:PVAc of 1:8.7 or 11.5% NVF.

All paste collected from the stripper was re-stripped until a level of0.01 to 0.04% residual VAM was achieved.

Run 3. Synthesis of PVAc/1.2% PNVF

This run was similar to the previous runs except for lower NVF andcatalyst ratios.

    ______________________________________                                        Initial Charges (g) Reactor I                                                                              Reactor II                                       ______________________________________                                        N-vinyl formamide (75% basis)                                                                     6.24     2.15                                             Vinyl acetate (distilled)                                                                         461.8    248                                              Methanol            1001     1084                                             Lupersol 10         0.18     0.18                                             Tartaric Acid       0.02     0.02                                             ______________________________________                                        Feeds              g/h     mL/h                                               ______________________________________                                        1.     Vinyl acetate (dist)                                                                          400     435                                                   NVF (dist., 75% purity)                                                                       6.24                                                   2.     Methanol        150     189.6                                                 Lupersol 10     0.63                                                   3.     Methanol        107     135.6                                                 Tartaric acid   0.012                                                  4.     Vinyl acetate   10      13.2                                                  NVF             2.15                                                   ______________________________________                                    

At steady state the free monomer was 23.6-30.9% in reactor I and16.3-30.9% in reactor II. Solids were about 28%. Residual unreacted NVFwas 0.19%. NMR indicated a PNVF content of 1.2%.

EXAMPLE II

This example demonstrates the hydrolysis of PVAc/PNVF to PVOH/PNVF andthe subsequent hydrolysis to PVOH/PVAm.

In general, PVAc/PNVF paste was added to a flexible plastic bag. KOH(0.01 eq. on VAc) dissolved in methanol was added to the bag withthorough mixing. The bag was sealed and heated at 60° C. in a water bathfor 15 minutes, precipitating the polymer as a white rubbery slab.

The PVOH/PNVF "slab" was mechanically ground into small pieces, theground polymer was added to a round-bottom flask equipped withmechanical stirrer, temperature controlled heating mantle, nitrogenblanket, thermometer, and condenser. Methanol was added to the flask togive about 15% polymer slurry by weight. (An attempt to hydrolyzePVOH/PNVF in methanol containing 10% deionized water resulted inslightly higher percent hydrolysis.) KOH (1.2 eq. on NVF) dissolved inmethanol was added to the slurry. The slurry was stirred vigorously andheated to reflux (63° C.) for 12 hours after which the slurry was cooledto ambient, filtered, washed with methanol and dried at 60° C. underhouse vacuum.

Run 4A. Hydrolysis of PVAc/6% PNVF to PVOH/6% PNVF. KOH (0.0045 g;0.0001 mol; 0.04 mol % on VAc) was dissolved in 5 mL of methanol andadded to PVAc/6% PNVF prime paste (50 g paste; 18.5 g of solid; 0.23mol) with thorough mixing. The solution was poured into a plastic bag.The bag was sealed and heated at 50° C. in a water bath for 2.0 h withno change in appearance. KOH (0.11 g; 0.002 mol; 1.0 mol % on VAc) wasdissolved in 5 mL of methanol and added to the bag with thorough mixing.The bag was re-sealed and placed in the water bath at 50° C.,immediately precipitating the polymer as a white rubbery slab. After 15min., heating was discontinued and the slab was removed from the bag,mechanically ground, washed with methanol, decanted, then stored underfresh MeOH. Molecular weight measurements gave Mn=23,000, Mw=44,000 forPVOH/6% PNVF.

Run 4B. Slurry Hydrolysis of PVOH/6% PNVF to PVOH/6% PVAm. To a 100 mLround-bottom flask equipped with mechanical stirrer, heating mantle, N₂blanket, thermometer and thermowatch were added the PVOH/PNVF polymer(Run 4A) and 75 mL of methanol. KOH (1.05 g; 0.0187 mol; 1.36 eq. onoriginal NVF) was dissolved in 5 mL of methanol and added to the slurry.The slurry was heated with vigorous stirring at reflux (63° C.) for 3.25h. Base consumption was monitored by potentiometric titration of 5 mLaliquots (MeOH-based solution) with approximately 0.1M HCl to pH=7.After heating for 3.25 h, the slurry volume was low due to evaporationof methanol and removal of aliquots for titration. Heating wasdiscontinued and the slurry was cooled overnight.

The following day, 50 mL of methanol was added. The slurry was reheatedwith vigorous stirring at reflux for 5 h. Base consumption was monitoredas above. The slurry was then cooled, filtered, washed with methanol anddried at 60° C. under house vacuum to give 6.6 g of oven dried material.This product showed complete PVAc hydrolysis and 77% PNVF hydrolysis.

Run 5. Attempted One-Step Hydrolysis of PVAc/6% PNVF to PVOH/6% PVAm inMethanol

A. NaOH (0.25 g; 0.0063 mol; 0.077 eq. on VAc; 1.2 eq. on NVF) wasdissolved in 5 mL of methanol and added to PVAc/6% PNVF in MeOH solution(7.4 g of polymer; 0.087 mol) with stirring, giving a viscous solution.The solution was poured into a 40 mL parr reactor. The solutionprecipitated giving a white slurry. The Parr reactor was sealed andheated 3 h at 80° C. (pressure ˜20 psi). The solid white polymer wasremoved from the reactor, mechanically ground into small pieces andwashed with methanol. The polymer was dried on a rotary vacuumevaporator, giving 3.9 g of dry polymer (0.0888 mol; 102% yield) andanalyzed by NMR in DMSO-d6: essentially no polymer bound acetate oracetamide, 5% PNVF remaining.

B. KOH (0.35 g, 0.0062 mol; 0.076 eq. on VAc, 1.2 eq. on NVF) wasdissolved in 5 mL of methanol and added to PVAc/6% PNVF MeOH solutionpolymer (7.4 g polymer; 0.087 mol) and treated as above. Dry polymer,4.0 g, was obtained (0.091 mol; 1.05% yield), NMR (DMSO-d6): PVOH/5.4%PNVF.

Run 6A. Hydrolysis of PVAc/12% PNVF to PVOH/12% PNVF

PVAc/12% PNVF (3396 g of paste at 40.3% solids and 374.6 g of paste at41.0% solids; 18.07 mol) was added to 6 plastic bags in approximatelyequal amounts. KOH (0.01 eq on VAc; 10.1 g) dissolved in methanol wasadded to each bag with thorough mixing. The bags were sealed and heatedat 60° C. in a water bath for 15 min, precipitating the polymer as awhite, rubbery slab. The slabs were stored overnight under methanol,then mechanically ground, washed with methanol, then stored overnightunder fresh methanol. Molecular weight measurements gave Mn=21,000,Mw=45,000 for PVOH/12% PNVF.

Run 6B. Slurry Hydrolysis of PVOH/12% PNVF to PVOH/12% PVAm

The polymer slurry from Run 7A was filtered to remove the excessmethanol. The ground polymer slabs and 5550 g of fresh methanol werethen added to a 12 L round-bottom flask equipped with mechanicalstirrer, heating mantle, N₂ blanket, thermometer, thermowatch andsolution withdraw tube. KOH (2.6 mol; 146.0 g; 1.2 eq on original NVF)was dissolved in 209.6 g of methanol and added to the slurry. The slurrywas stirred vigorously and heated at reflux (63° C.) for 12 h. Baseconsumption was monitored by potentiometric titration of 5 mL aliquotsof the reaction solution with 0.12M HCl to pH=7.

    ______________________________________                                        Percent Hydrolysis of NVF by Potentiometric Titration                         Hours at Reflux                                                                              % Hydrolysis of NVF                                            ______________________________________                                         0 (ambient)   26.3                                                            0 (just at reflux)                                                                          39.7                                                            1.5           64.3                                                            3.0           72.1                                                            3.0           72.1                                                            4.5           76.5                                                           12.0           84.3                                                           ______________________________________                                         *5 mL aliquots titrated with 0.1 N HCl.                                  

The slurry was then cooled, filtered, washed with methanol and dried at60° C. under house vacuum to give 866.2 g of oven dried material. Thisproduct showed complete PVAc hydrolysis and 80% PNVF hydrolysis by NMR.

EXAMPLE III

The following is an example for the preparation of PVOH/PVAm fromPVAc/PVNF with intermediate drying of PVOH/PNVF:

To a 250 mL 3-neck round-bottom flask equipped with mechanical stirrer,N₂ purge, thermometer, thermowatch and heating mantle, were addedPVAc/1.2% PNVF (90.0 g at 16.7% solids, 0.19 mol). The paste was heatedwith vigorous agitation to 60° C. under N₆. At 60° C. NaOH was added (asa 50% soln) and the sample was stirred for 15 min. The white polymerslurry was concentrated to a dry powder on a rotary evaporator,reslurried in methanol and again concentrated to a dry powder. Thepolymer was checked by GLPC for the absence of methyl acetate,reslurried in methanol (100 mL) in a 250 mL 3-neck round-bottom flaskequipped as previously described. To the slurry was added NaOH (1.04 gof 50% solution, 0.0130 mol) and the slurry was heated at reflux (65°C.) for 4 h. The polymer was collected by filtration, washed with ˜100mL of methanol, and dried at 60° C. under house vacuum. Average yieldwas 86%. The product showed complete PVAc hydrolysis and 96% PNVFhydrolysis by NMR.

EXAMPLE IV

This example illustrates the hydrolysis of PVOH/PNVF to PVOH/PVAm underone-phase conditions.

KOH (0.79 g; 0.0141 mol; 1.0 mol % on VAc) was dissolved in 10 mL ofmethanol and added to PVAc/12% PNVF (327 g paste; 135.1 g of solids;3.21 mol) with thorough mixing in two plastic bags. The bags were sealedand heated at 60° C. in a water bath for 15 min, giving a white polymerslab. The slab was removed from the bag, cut into small pieces, washedwith methanol and dried at 60° C. under house vacuum; 156 g of ovendried material was obtained. Molecular weight measurements gaveMn=21,000, Mw=45,000 for PVOH/12% PNVF.

To a 2 L round-bottom flask equipped with a heating mantle, mechanicalstirrer, condenser, N₂ blanket, thermometer and thermowatch were addedPVOH/PNVF from above (104 g dried material; 2.96 mol) and water (1260g).KOH (21.9 g; 0.390 mol; 1.1 eq. on NVF) was dissolved in 20 ml of waterand added to the polymer mixture. The mixture was heated at 80° C. withvigorous stirring for 3.0 h, giving a viscous solution. PVOH/12% PVAmwas isolated by precipitating out of MeOH. Yield: 113 g oven driedmaterial obtained. This product showed complete PVAc hydrolysis and 93%PNVF hydrolysis by NMR.

EXAMPLE V

This example illustrates the slurry, acid hydrolysis of PVOH/PNVF toPVOH/PVAm.

Run 7A. Slab Hydrolysis of PVAc/12% PNVF

KOH (0.0064 mol; 0.36 g; 0.01 eq. on VAc) was dissolved in 20 ml ofmethanol and added to 150 g of PVAc/12% PNVF prime paste (0.73 mol; 61.5g) with thorough mixing in a plastic bag. The bag was sealed and heatedat 60° C. in a water bath for 15 min; precipitating the polymer as awhite rubber slab. The slab was removed from the bag, mechanicallyground into small pieces on a grinder, washed with methanol, then storedovernight under fresh methanol.

Run 7B. Slurry, Acid Hydrolysis of PVOH/12% PNVF

The above polymer slurry was filtered to remove the excess methanol. Theground polymer and 250 g of fresh methanol were then added to a 1 Lround bottom flask equipped with mechanical stirrer, heating mantle,nitrogen blanket, thermometer, thermowatch and condenser withdistillation trap. HCl (0.105 mol; 3.83 g; 1.2 eq. on NVF) was added tothe slurry. The slurry was stirred vigorously and heated reflux for 12h. Acid consumption was monitored by potentiometric titration of 3 mLaliquots of the reaction solution with 0.1 % NaOH to pH 7. The slurrywas cooled to ambient, and washed with methanol and dried at 60° C.under house vacuum to give 31.4 g of polymer. NMR analysis indicatedcomplete hydrolysis.

    ______________________________________                                        Hydrolysis of PVOH/PNVF in Methanol/HCl                                       Hours at 68° C.                                                                        NaOH (ml)                                                     ______________________________________                                        Ambient         6.0                                                           0               4.2                                                           1               3.0                                                           3               1.7                                                           6               1.4                                                           12              1.3                                                           ______________________________________                                    

EXAMPLE VI

This example illustrates an essentially one step process for batchpreparation of PVOH/PVAm under basic conditions as a powder productwithout a grinding step and without removal of methyl acetate.

To a 250 ml 3-necked round bottom flask equipped with condenser,mechanical stirrer and catalyst feed tube were added 60 g of methanoland 100 g of PVAc/6% PNVF paste (15.88% solid). The resulting solutionwas heated to 65° C., and KOH (0.1986 g; 0.02 eq. on VAc) in 10 g ofmethanol was then added into the polymer solution over 1 h. The polymerprecipitated as a white polymer powder near the end of catalystaddition. After stirring the polymer slurry for 1/2 h at 65° C., KOH(0.942 g; 1.5 eq. on NVF) in a 20 g of methanol was added in. Theresulting slurry was stirred vigorously and heated at 65° C. for 12 hr.The slurry was cooled to ambient, and filtered, washed with methanol anddried at 60° C. under house vacuum to give 8.2 g of polymer. NMRanalysis indicated complete hydrolysis of PVAc and 82% hydrolysis ofPNVF.

EXAMPLE VII

This example illustrates the improvement in the speed and efficiency ofthe PVOH/PNVF hydrolysis in methanol containing water.

Preparation of PVOH/12% PNVF. PVAc/12% PNVF (600 g of paste at 46.5%solids=279 g; 3.32 mol) was added to 2 plastic bags in equal amounts.KOH (0.01 eq on VAc; 1.64 g) dissolved in methanol was added to each bagwith thorough mixing. The bags were sealed and heated at 60° C. in awater bath for 15 min., precipitating the polymer as white rubberyslabs. The slabs were softer than usual and imparted a pale yellow colorto the methanol wash. 'H MNR analysis of a dry sample indicated 6.9 mol% of the polymer was unhydrolyzed vinyl acetate.

The slabs were mechanically ground into small pieces and divided intothree approximately equal parts. Each part was washed and soakedovernight in a methanol solution containing 1% water (A), 5% water (B),or 10% water (C).

Preparation of PVOH/12% PVAm. The polymer slurries were separatelyfiltered to remove the excess methanol/water solution. The wet polymersamples were added to separate 1 L round-bottom flasks each equippedwith a mechanical stirrer, heating mantle. N₂ blanket, thermometer,thermowatch and condenser. Solvent was added to each flask as shown onthe table:

    ______________________________________                                        % Water                   G Dry                                               In Methanol Approx. Volume                                                                              Polymer  % Yield                                    ______________________________________                                        A    1          566 ML        38.9   81.2                                     B    5          566 ML        37.2   77.7                                     C    10         590 ML        38.2   79.8                                     ______________________________________                                    

KOH (1.2 eq on original NVF; 0.160 mol 8.97 g) dissolved in methanol wasadded to each slurry. The slurries were stirred vigorously and heated toreflux (63° C.) for 12 h. Base consumption was monitored bypotentiometric titration of 3 mL aliquots of the reaction solution with0.12M HCl to pH=7. After 12 h. at reflux, each slurry was cooled toambient, filtered, washed with methanol and dried at 60° C. under housevacuum.

The results show that hydrolysis rate and extent increased withincreasing water addition to the methanol.

    ______________________________________                                        Calculated % Hydrolysis of NVF By Titration                                   % Water           Just at  Hrs. At Reflux                                     In Solvent                                                                             Ambient  Reflux   1    3     6    12                                 ______________________________________                                        1    (A)     38.4     40     70.7 82.7  89.5 92.5                             5    (B)     36.7     36.7   75.8 82.6  89.5 96.3                             10   (C)     26.1     38.5   77.5 86.4  91.7 98.8                             ______________________________________                                    

B and C showed 93% hydrolysis by 'H MNR analysis. The lack of agreementwith the titration results may reflect partial reaction of KOH withresidual acetate groups in this polymer.

STATEMENT OF INDUSTRIAL APPLICATION

The two phase hydrolysis of poly(vinyl alcohol)-co-poly(vinylamide)yields poly(vinyl alcohol)/poly(vinylamine) which can be used in thepreparation of a paperboard product by depositing wood pulp from anaqueous slurry containing an effective amount of a moist compressivestrength additive mixture consisting essentially of the poly(vinylalcohol)/poly(vinylamine) and, optionally, an anionic polymer such ascarboxymethyl cellulose.

We claim:
 1. A method for making a poly(vinylalcohol)-co-poly(vinylamine) which comprises(a) continuously feedingvinyl acetate monomer and N-vinyl formamide monomer into a reactionmixture in a reaction vessel, (b) copolymerizing the vinyl acetate andN-vinyl formamide monomers to yield poly(vinyl acetate)-co-poly(N-vinylformamide) in the reaction mixture, (c) continuously withdrawing fromthe reaction vessel reaction mixture containing the poly(vinylacetate)-co-poly(N-vinyl formamide), (d) hydrolyzing the acetatefunctionality of the poly(vinyl acetate)-co-poly(N-vinyl formamide) in amethanolic medium to yield poly(vinyl alcohol)-co-poly(N-vinylformamide) as a gel swollen with methanol and methyl acetate, (e)comminuting the gel to a particulate copolymer product, and (f)hydrolyzing the copolymer particles as a slurry in methanol under acidor base conditions to yield poly(vinyl alcohol)-co-poly(vinylamine)particles.
 2. The method of claim 1 in which the hydrolysis of step (f)is performed using base to yield salt free particles of the vinylaminecopolymer.
 3. The method of claim 1 in which the hydrolysis of step (f)is performed using acid to yield particles of the corresponding acidsalt of the vinylamine copolymer.
 4. The method of claim 1 in which thepoly(vinyl alcohol)-co-poly(vinylamide) is represented by the followingformula ##STR5## wherein m is 0 to 15 mole %,n is 50 to 99 mole %, and xis 1 to 50 mole %.
 5. The method of claim 4 in which the hydrolysisyields a copolymer of the following formula ##STR6## wherein m is 0-15mole %,n is 50-99 mole % x is 0-30 mole %, and y is 1-50 mole %.
 6. Themethod of claim 3 in which the poly(vinyl alcohol-co-poly(vinylamide) isrepresented by the following formula ##STR7## wherein m is 0 to 15 mole%,n is 50 to 99 mole %, and x is 1 to 50 mole %.
 7. The method of claim6 in which the hydrolysis yields the corresponding acid salt of acopolymer of the following formula ##STR8## wherein m is 0-15 mole %,nis 50-99 mole % x is 0-30 mole %, and y is 1-50 mole %.
 8. The method ofclaim 1 including(g) washing the poly(vinyl alcohol)-co-poly(vinylamine)with methanol and removing the methanol from the copolymer.
 9. Themethod of claim 1 in which the particulate copolymer product of step (e)is rinsed with methanol prior to the hydrolyzing of step (f).